function draw_f2( )

    global S_Map;

    figure(f2);
    
    X(1,:)=S_Map(:,1);     % node's X coordinate
    Y(1,:)=S_Map(:,2);
    Z(1,:)=S_Map(:,4)-S_Map(:,3)+S_Map(:,6);  % surface visualising instant energy value in each node

    %Z(1,:)=S_Map(:,3)+S_Map(:,6);  % surface visualising instant energy value in each node

    g=gridfit(X,Y,Z,gx,gy);
    surf(gx,gy,g);             % wykres powierzchni 3D (X,Y,Z)
    lighting phong          % inne opcje: flat, gouraud, none
    shading interp          % cieniowanie 
    plot3(X,Y,Z,'black.'); 

end

